Landlord that only raise their rents every several years to catch up are more likely to force tenants to consider leaving.If you want to keep your tenants indefinitely simply never raise their rents. 

Tell them yes you start it after 5 days but that's to protect yourself if they aren't going to pay ever so you don't get stuck paying their way indefinitely.

Those criteria will be defensible in court.Alternatively, you can "pocket veto" them by just indefinitely considering them.  

Now if he doesn't leave she may lose her deposit to you but and you may need to go to court to evict him but you do not have her on the hook indefinitely if he does not vacate.  

So, I would give them written permission for the lover to be an indefinite guest, as long as there weren't any problems, and that this permission could be rescinded if there were.Now, technically, the lover becomes a tenant once they begin living there - it establishes tenancy.  

(After any rehabbing work if needed to be done)    After returning the investor's initial investment, does the investor continue to receive a % of the proceeds (if cash flowing) indefinitely or only until a specified amount is achieved (similar to question 1)Again, understand each deal is different and there's no standardized format.

The defensive virtues are the depreciation and tax code benefits allotted for investing in incentivized areas and / or using vehicles like Self Directed IRAs that can defer tax liability indefinitely and wash it entirely upon your passing as the monies flow to your children or loved ones.

If you use the personal car, make sure to keep detail record so that CPA can prorate the expenses between personal and business.This can include- oil changes, Maintenance, gas, repairs, parking, tolls, and depreciation.

Or will they run it for you indefinitely and permanently take a cut/fee from your earnings?

It will eventually sort itself out and they won't be able to stay in the property indefinitely.